Semiconductor device and light-emitting device

ABSTRACT

One feature of a semiconductor device of the present invention is to include an electrode that serves as an electrode of a light-emitting element. The electrode includes a first layer and a second layer. Further, end portions of the electrode are covered with a partition layer having an opening portion. Moreover, a part of the electrode is exposed by the opening portion of the partition layer. One feature of a semiconductor device of the present invention is to include an electrode that serves as an electrode of a light-emitting element and a transistor. The electrode and the transistor are connected electrically to each other. The electrode includes a first layer and a second layer. Further, end portions of the electrode are covered with a partition layer having an opening portion. Moreover, the second layer is exposed by the opening portion of the partition layer.

This application is a divisional of application Ser. No. 12/727,386filed on Mar. 19, 2010 now U.S. Pat. No. 8,174,178 which is a divisionalof application Ser. No. 11/254,394 filed on Oct. 20, 2005 (now U.S. Pat.No. 7,683,532 issued Mar. 23, 2010).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device that can be usedfor manufacturing a light-emitting device, specifically, a structure ofa semiconductor device.

2. Description of the Related Art

In recent years, a light-emitting device having a display function hasbeen developed actively. In such light-emitting devices, alight-emitting element is used for a pixel. In a light-emitting devicewhich can display by active matrix driving among the light-emittingdevices, a circuit including transistors and the like for driving thelight-emitting element is provided, in addition to the light-emittingelement. Such a light-emitting device is formed by forming a substrateprovided with a circuit and the like, and then, forming a light-emittingelement over the substrate as described by Reference 1 (Reference 1:Japanese Patent Laid-Open No. 2001-189192).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductordevice that can be used for forming a light-emitting device that doesnot cause defects such as a short circuit between electrodes in alight-emitting element.

One feature of the present invention is to include an electrode servingas an electrode of a light-emitting element. The electrode includes afirst layer and a second layer. And end portions of the electrode arecovered with a partition layer (also, referred to as a bank) having anopening portion. A portion of the electrode is exposed in the openingportion of the partition layer.

One feature of the present invention is to include an electrode servingas an electrode of a light-emitting element and a transistor. Theelectrode is electrically connected to the transistor. The electrodeincludes a first layer and a second layer. And end portions of theelectrode are covered with a partition layer having an opening portion.The second layer is exposed in the opening portion of the partitionlayer.

One feature of the present invention is to include a plurality ofcombinations of a transistor and an electrode. The electrode serves asan electrode of a light-emitting element. In each combination, thetransistor is electrically connected to the electrode. The electrodeincludes a first layer and a second layer, and the thickness of thesecond layer is different in each combination. The end portions of theelectrode are covered with a partition layer having an opening portion.The second layer is exposed in the opening portion of the partitionlayer.

In the above described semiconductor device according to the presentinvention, the first layer is a layer formed using a conductivesubstance. In addition, the second layer includes a metal oxide and anorganic compound. As the metal oxide, either a substance showingelectron accepting property to a hole transporting substance or asubstance showing electron donating property to an electron transportingsubstance is preferably used. In addition, as the organic compound,either a hole transporting substance or an electron transportingsubstance is preferably used. The hole transporting substance herein isa substance that has a property of transporting holes rather thanelectrons. In addition, the electron transporting substance is asubstance that has a property of transporting electrons rather thanholes. When the metal oxide is a substance showing electron acceptingproperty to a hole transporting substance in the second layer, theorganic compound is preferably the hole transporting substance. Further,when the metal oxide is a substance showing electron donating propertyto an electron transporting substance in the second layer, the organiccompound is preferably the electron transporting substance.

According to the present invention, a semiconductor device including anelectrode that has a favorable smoothness and that can be used as anelectrode of a light-emitting element, can be provided.

By using a semiconductor device of the present invention, alight-emitting device in which defects such as a short circuit betweenelectrodes of a light-emitting element are reduced, can be manufactured.In addition, an optical path length of light can be adjusted so thatlight can be extracted from each light-emitting element with good colorpurity by using a semiconductor device according to the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows one mode of a semiconductor device according to one aspectof the present invention;

FIGS. 2A to 2C each show one mode of a light-emitting device formed byusing a semiconductor device of the present invention;

FIG. 3 shows one mode of a semiconductor device according to one aspectof the present invention;

FIG. 4 shows one mode of a semiconductor device according to one aspectof the present invention;

FIG. 5 shows one mode of a semiconductor device according to one aspectof the present invention;

FIG. 6 shows one mode of a light-emitting device formed by using asemiconductor device of the present invention;

FIGS. 7A to 7C each show one mode of a light-emitting device to whichthe present invention is applied;

FIG. 8 shows one mode of a light-emitting device to which the presentinvention is applied;

FIG. 9 shows a circuit included in a light-emitting device to which thepresent invention is applied;

FIG. 10 is a top view showing one mode of a light-emitting device towhich the present invention is applied;

FIG. 11 shows one mode of a frame operation of a light-emitting deviceapplied the present invention;

FIGS. 12A to 12C each show one mode of an electronic device to which thepresent invention is applied;

FIG. 13 shows one mode of a semiconductor device according to one aspectof the present invention;

FIGS. 14A and 14B each show one mode of a layer structure of alight-emitting element included in a light-emitting device to which thepresent invention is applied;

FIGS. 15A and 15B each show one mode of a layer structure of alight-emitting element included in a light-emitting device to which thepresent invention is applied;

FIGS. 16A and 16B each show one mode of a layer structure of alight-emitting element included in a light-emitting device to which thepresent invention is applied; and

FIGS. 17A and 17B each show one mode of a layer structure of alight-emitting element included in a light-emitting device to which thepresent invention is applied.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment Modes according to the present invention will hereinafter bedescribed. The present invention can be carried out in many differentmodes, and it is easily understood by those skilled in the art thatmodes and details herein disclosed can be modified in various wayswithout departing from the spirit and the scope of the presentinvention. Therefore, it should be noted that the present inventionshould not be interpreted as being limited to the description of theembodiment modes to be given below.

Embodiment Mode 1

A semiconductor device according to the present invention is describedwith reference to FIG. 1. An insulating layer 102 is provided over asubstrate 101. A transistor 111 including a semiconductor layer 103, agate insulating layer 104, and a gate electrode 105 is provided over theinsulating layer 102. The transistor 111 is covered with an insulatinglayer 106 having an opening portion. Conductive layers 107 a and 107 bare provided over the insulating layer 106. In addition, the conductivelayers 107 a and 107 b are in contact with the semiconductor layer 103through the opening portion provided in the insulating layer 106 and thegate insulating layer 104. It should be noted that the portions of thesemiconductor layer 103 that are in contact with the conductive layers107 a and 107 b contain impurities at a high concentration. Theconductive layers 107 a and 107 b are covered with an insulating layer108 having an opening portion. And an electrode 109 including a firstlayer 109 a and a second layer 109 b is provided over the insulatinglayer 108. The electrode 109 is in contact with the conductive layer 107a through the opening portion provided in the insulating layer 108. Inother words, the electrode 109 is electrically connected to thetransistor 111 through the conductive layer 107 a. In addition, endportions of the electrode 109 are covered with a partition layer 110.

The first layer 109 a is not necessarily limited. A conductive substancesuch as indium tin oxide, indium tin oxide including silicon oxide,aluminum, tungsten, tantalum nitride, copper, chromium, titanium ortantalum can be used regardless of a work function of a substance to beused. For example, when light is to be extracted outside through theelectrode 109, the first layer 109 a may be formed using indium tinoxide, indium tin oxide including silicon oxide, or the like and visiblelight may be extracted through the electrode 109. In addition, whenlight is reflected from the electrode 109, the first layer 109 a may beformed using aluminum or the like.

The second layer 109 b includes a metal oxide and an organic compound.The metal oxide is preferably a substance selected from a substanceshowing electron accepting property to a hole transporting substance anda substance showing electron donating property to an electrontransporting substance. As specific examples of such a substance, alkalimetal oxide, alkaline-earth metal oxide and the like such as lithiumoxide, calcium oxide, magnesium oxide, sodium oxide and the like aregiven as well as molybdenum oxide, vanadium oxide, ruthenium oxide,cobalt oxide, copper oxide and the like. A substance selected from ahole transporting substance and an electron transporting substance ispreferable. The hole transporting substance here is a substance havingproperty of transporting holes rather than electrons, preferably asubstance having hole mobility of 10⁻⁶ cm²/Vs or more. In addition, theelectron transporting substance is a substance having property oftransporting electrons rather than holes, preferably a substance havingelectron mobility of 10⁻⁶ cm²/Vs or more. As specific examples of thehole transporting substance, an aromatic amine compound such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD),4,4′,4″-tris(N,N-diphenylamino)triphenylamine (TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MTDATA),and 4,4′-bis{N-[4-(N,N-di-m-tolylamino)phenyl]-N-phenylamino}biphenyl(DNTPD); a phthalocyanine compound such as phthalocyanine (H₂Pc), copperphthalocyanine (CuPc) and vanadyl phthalocyanine (VOPc) can be used.Among them, an aromatic amine compound is preferably used. Note thataromatic amine compound is a compound including a structure shown by thefollowing structural formula (1). By using an aromatic amine compound,accepting and donating of electrons between the hole transportingsubstance and the substance showing electron accepting property to thehole transporting substance are conducted more smoothly.

In addition, as specific examples of an electron transporting substance,a metal complex such as tris(8-quinolinolato)aluminum (Alq₃),tris(4-methyl-8-quinolinolato)aluminum (Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (BeBq₂),bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (BAlq),bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (Zn(BOX)₂),bis[2-(2-hydroxyphenyl)benzothiazolate]zinc (Zn(BTZ)₂) can be used. Inaddition, the following substances can be used as the substance havingelectron transporting property:2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD);1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7);3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (TAZ);3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(p-EtTAZ); bathophenanthroline (BPhen); bathocuproin (BCP); and thelike.

The thickness of the second layer 109 b is not necessarily limited;however, it is preferably 50 to 1000 nm, more preferably 100 to 300 nm.Unevenness of the surface of the first layer 109 a can be reduced byadopting such a thickness. It should be noted that the second layer 109b is a layer that has a smoothing property since it includes a metaloxide and thus, the organic compound is not easy to be crystallized. Asjust described, the electrode 109 in which the second layer 109 b isstacked on the first layer 109 a has a high smoothing property. Thus,when a different layer is stacked over the first electrode 109, it canbe stacked with favorable coverage, or without disconnection between thefirst electrode 109 and the different layer.

The combination of a metal oxide and an organic compound is preferably acombination of a hole transporting substance and a substance showingelectron accepting property to the hole transporting substance or anelectron transporting substance and a substance showing electrondonating property to the electron transporting substance. By combining ametal oxide and an organic compound, electrons or holes are easilygenerated from the electrode 109.

As described above, the electrode 109 in which the first layer 109 a andthe second layer 109 b are stacked can be used as the electrode of thelight-emitting element. By using a semiconductor device having theelectrode 109 like the semiconductor device in this embodiment mode, afavorable light-emitting device can be manufactured in which defectssuch as a short circuit between electrodes of the light-emitting elementdue to unevenness of the electrode 109 are reduced. In addition, endportions of the electrode 109 are covered by a partition layer 110 as inthe semiconductor device of this embodiment mode. Thus, defects of alight-emitting element such as a short circuit due to a concentratedelectric field in the end portions of the electrode 109 can beprevented; therefore, a favorable light-emitting device can bemanufactured. In a semiconductor device of the present invention, theelectrodes 109 corresponding to each light-emitting element are providedseparately from each other, and thus crosstalk is not caused betweenadjacent electrodes 109, and in particular, it is effective formanufacturing a light-emitting device having high-definition pixels.

The substrate 101 is not necessarily limited, and a flexible substratesuch as polyethylene terephthalate (PET) or polyethylene naphthalate(PEN) can be used, in addition to a glass substrate or a quartzsubstrate.

The insulating layer 102 is not necessarily limited, and an insulatorsuch as silicon oxide and silicon nitride can be used. The insulatinglayer 102 may be a single layer or a multilayer in which a plurality oflayers are stacked. By providing the insulating layer 102 between thesubstrate 101 and the transistor 111, diffusion of impurities from thesubstrate 101 to the transistor 111 can be prevented.

The transistor 111 is not necessarily limited and either a single gatetype transistor or a multigate type transistor having a plurality ofgate electrodes may be used. In addition, a transistor having an LDDstructure in which an impurity region having a concentration lower thana drain is formed between a channel forming region and the drain may beused. Further, a transistor having a gate-overlapped LDD structure inwhich a low concentration impurity region formed between a channelforming region and a drain is overlapped with a gate electrode may beused. A top gate type transistor or a bottom gate type transistor may beused.

The semiconductor layer 103, the gate insulating layer 104 and the gateelectrode 105 included in the transistor 111 are not necessarilylimited.

In addition, the semiconductor layer 103 may be formed using asemi-amorphous semiconductor. The semi-amorphous semiconductor is asemiconductor that has an intermediate structure between an amorphousstructure and a crystalline structure (including a single crystal and apolycrystal) and a third state which is stable in terms of free energy,and it includes a crystalline region having short-range order andlattice distortion. At least a part of a region in the film contains acrystal grain of 0.5 nm to 20 nm. A Raman spectrum is shifted to a lowerwavenumber side than 520 cm⁻¹. Diffraction peaks of (111) and (220) tobe caused by a crystal lattice of silicon are observed in X-raydiffraction. Hydrogen or halogen of 1 atomic % or more is included toterminate dangling bonds. It is also referred to as a microcrystalsemiconductor. A silane gas (Si_(n)H_(2n+2), such as SiH₄ and Si₂H₆),SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like are decomposed by glowdischarge (plasma CVD) to form the semi-amorphous semiconductor. The gasmay be diluted with H₂, or H₂ and one or more rare gas elements ofhelium, argon, krypton, and neon. A dilution ratio thereof may rangefrom 2 to 1000 times; pressures, approximately 0.1 Pa to 133 Pa; powersupply frequency, 1 MHz to 120 MHz, preferably, 13 MHz to 60 MHz. Asubstrate heating temperature may be 300° C. or less, preferably, 100 to250° C. An impurity concentration of an atmospheric constituent impuritysuch as oxygen, nitrogen, or carbon, as an impurity element in the film,is preferably 1×10²⁰/cm³ or less; specifically, the concentration ofoxygen is 5×10¹⁹/cm³ or less, preferably 1×10¹⁹/cm³ or less. Note thatthe crystallinity of the semiconductor layer 103 has no limitations, forexample, the semiconductor layer 103 may be a layer formed using asemiconductor such as silicon or silicon germanium.

The gate insulating layer 104 can be formed using an insulator such assilicon oxide or silicon nitride. The silicon oxide may contain a slightamount of nitrogen and the silicon nitride may contain a slight amountof oxygen. The gate insulating layer 104 may be formed with a singlelayer of an insulating layer or a multilayer in which a plurality ofinsulating layers are stacked.

The gate electrode 105 can be formed using a metal nitride such astantalum nitride or titanium nitride, in addition to metals such astungsten, aluminum, molybdenum or copper. In addition, the gateelectrode 105 may be formed with a single layer of a conductive layer ora multilayer in which a plurality of conductive layers are stacked. Forexample, as shown in FIG. 13, the gate electrode 105 may have astructure in which the conductive layer 105 a and the conductive layer105 b are stacked. In the structure, the sides of the conductive layer105 b are further in from the sides of the conductive layer 105 a. Theconductive layers 105 a and 105 b each may have an angled side. Theconductive layers 105 a and 105 b are formed using different substances.

The conductive layers 107 a and 107 b have no limitations in particular,and can be formed using a metal nitride such as tantalum nitride ortitanium nitride, in addition to a metal such as tungsten, aluminum,molybdenum or copper. The conductive layers 107 a and 107 b may beformed with a single layer of an insulating layer or a multilayer inwhich a plurality of insulating layers are stacked.

The insulating layers 106 and 108 does not have limitations inparticular and can be formed using an insulator such as silicon oxide orsilicon nitride. The silicon oxide may contain a slight amount ofnitrogen and the silicon nitride may contain a slight amount of oxygen.The silicon nitride may include hydrogen. The insulating layers 106 and108 may be formed using an organic compound such as acrylic orpolyimide, or an insulator such as siloxane. Note that siloxane is acompound that includes elements such as silicon (Si), oxygen (O) andhydrogen (H), and Si—O—Si bond (siloxane bond) (H may be substituted byalkyl group or aryl group). By using acryl, polyimide, siloxane or thelike, an insulating layer having a flat surface can be formed like theinsulating layer 108 shown in FIG. 1. The insulating layers 106 and 108may be formed with a single layer of an insulating layer or a multilayerin which a plurality of insulating layers are stacked.

The partition layer 110 has no limitations and is preferably formed sothat the side of the partition layer can have a shape with a curvature.The partition layer 110 may be formed using silicon oxide, siliconnitride, siloxane or the like, in addition to an organic compound suchas acryl, polyimide or resist.

Embodiment Mode 2

One mode of a light-emitting element manufactured using a semiconductordevice of the present invention as described in Embodiment Mode 1 isdescribed with reference to FIGS. 2A to 2C.

FIG. 2A is a cross-sectional view of a semiconductor device according tothe present invention. Transistors 302, 303, 304 and 305 are formed overa substrate 301. The transistors 302 and 303 are both provided in apixel region over the substrate 301. The transistors 304 and 305 areprovided in a driver circuit region over the substrate 301. Thetransistors 302 to 305 are covered by an insulating layer 306 having anopening portion. A conductive layer that is processed into a desiredshape is provided over the insulating layer 306. Some conductive layers,e.g., conductive layers 307 to 309, each serve as a wiring for inputtinga signal or supplying current. The conductive layer 310 is formed tocover the opening portion of the insulating layer 306 and is connectedto the transistor 302. Further, the conductive layers 307 to 309 arecovered by an insulating layer 311 having an opening portion. Anelectrode 312 including a first layer 312 a and a second layer 312 b isformed over the insulating layer 311. The first layer 312 a and thesecond layer 312 b are stacked such that the first layer 312 a exists onthe insulating layer 311 side. The electrode 312 covers the openingportion of the insulating layer 311 and is connected to the conductivelayer 310. Further; end portions of the electrode 312 are covered by thepartition layer 313 and a part of the electrode 312 is exposed in theopening portion of the partition layer 313.

The first layer 312 a corresponds to the first layer 109 a and thesecond layer 312 a corresponds to the second layer 109 b. In addition,the transistor 302 corresponds to the transistor 111 and the insulatinglayer 306 corresponds to the insulating layer 106. The conductive layer310 corresponds to the conductive layer 107 a. In addition, theinsulating layer 311 corresponds to the insulating layer 108. Thepartition layer 313 corresponds to the partition layer 110.

A transistor 304 and a transistor 305 for a driver circuit, conductivelayers 307 to 309 or the like serving as a wiring or the like may beincluded in the semiconductor device, as in the semiconductor device asshown in FIG. 2A. In addition, a transistor 303 for a pixel circuit orthe like may be provided.

A method for manufacturing a light-emitting device using a semiconductordevice as shown in FIG. 2A is described.

First, a light-emitting layer 314 is formed to cover the electrode 312.An electrode 315 is formed over the light-emitting layer 314. Anoverlapping portion in which the electrode 312, the light-emitting layer314 and the electrode 315 serves as a light-emitting element 316.

The light-emitting layer 314 may be constituted so that light is emittedfrom a light-emitting substance when current can flow between theelectrode 312 and the electrode 315 and electrons and holes arerecombined. The light-emitting substance herein is a substance that hasa favorable emission efficiency and that can emit light of a desiredemission wavelength.

The method for forming the light-emitting layer 314 is not necessarilylimited, and any of an evaporation method, a sputtering method, aspin-coating method, an ink-jet method and the like may be used. Inaddition, the light-emitting layer 314 may be formed using an inorganicsubstance or the like in addition to an organic substance.

The light-emitting layer 314 is formed using a light-emitting substance.At this time, the light-emitting layer 314 may be formed such that alight-emitting substance is included to be dispersed in a layerincluding a substance having an energy gap larger than that of thelight-emitting substance. By dispersing the light-emitting substance,quenching of light due to the concentration can be prevented. Thelight-emitting substance has no limitations in particular. In order toobtain red light emission, substances that can emit light with a peak ofemission spectrum in 600 to 680 nm, can be used as a light-emittingsubstance. For example,4-dicyanomethylene-2-isopropyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(DCJTI);4-dicyanomethylene-2-methyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(DCJT);4-dicyanomethylene-2-tert-butyl-6-[2-(1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]-4H-pyran(DCJTB); periflanthene;2,5-dicyano-1,4-bis[2-(10-methoxy-1,1,7,7-tetramethyljulolidine-9-yl)ethenyl]benzeneand the like can be used. In order to obtain greenish light emission,substances that can emit light with a peak of emission spectrum in 500to 550 nm can be used as a light-emitting substance. F or example,N,N′-dimethylquinacridone (DMQd), coumarin 6, coumarin 545T,tris(8-quinolinolate)aluminum (Alq₃) and the like can be employed. Inorder to obtain bluish light emission, a peak of emission spectrum in420 to 500 nm can be used as a light-emitting substance. For example,9,10-bis(2-naphthyl)-2-tert-butylanthracene (t-BuDNA); 9,9′-bianthryl;9,10-diphenylanthracene (DPA); 9,10-bis(2-naphthyl)anthracene (DNA);bis(2-methyl-8-quinolinolate)-4-phenylphenolate-gallium (BGaq);bis(2-methyl-8-quinolinolate)-4-phenylphenolate-aluminum (BAlq); and thelike can be used. A substance to be used with a light-emitting substanceso as to disperse the light-emitting substance has no limitations, forexample, an anthracene derivative such as9,10-di(2-naphthyl)-2-tert-butylanthracene (t-BuDNA); a carbazolederivative such as 4,4′-bis(N-carbazolyl)biphenyl (CBP); a metal complexsuch as bis[2-(2-hydroxyphenyl)pyridinato]zinc (Znpp2) andbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (ZnBOX); and the like can beused.

The electrode 315 has no limitations in particular. The electrode 315may be formed using a conductive substance such as indium tin oxide,indium tin oxide including silicon, aluminum, tungsten, tantalumnitride, copper, chromium, titanium, tantalum, and tantalum nitride. Inaddition, the forming method of the electrode 315 is not necessarilylimited, and any of an evaporation method, a sputtering method, anink-jet method, a spin coating method and the like may be used.

A first transport layer 351 may be provided between the electrode 312and the light-emitting layer 314 as shown in FIG. 14A. FIG. 14A is anenlarged view of the overlapping portion of the electrode 312, thelight-emitting layer 314 and the electrode 315 (a portion surrounded bya dotted line in FIG. 14B). When holes are injected from the electrode312, the first transport layer 351 is preferably formed using a holetransporting substance. In addition, when electrons are injected fromthe electrode 312, the first transport layer 351 is preferably formedusing an electron transporting substance. In this manner, by providingthe first transport layer 351, the electrode 312 can be prevented frombecoming closer to the light-emitting layer 314; therefore, quenching oflight due to the metal included in the electrode 312 can be prevented.The first layer 351 may be a single layer or a multilayer including thefirst transport layer 351 a, the first transport layer 351 b or anotherlayer as shown in FIG. 15A. FIG. 15A is an enlarged view of theoverlapping portion of the electrode 312, the light-emitting layer 314and the electrode 315 (a portion surrounded by a dotted line in FIG.15B). When the first transport layer 351 is a multilayer and holes areinjected from the electrode 312, a layer including a hole transportingsubstance and a metal oxide such as molybdenum oxide, vanadium oxide orruthenium oxide, and a layer including only a hole transportingsubstance may be stacked. In particular, in the case where the holetransporting substance tends to be easily crystallized, crystallizationcan be prevented by including a metal oxide and a short circuit betweenelectrodes of the light-emitting element due to crystallization can beprevented. The interface between the first transport layer 351 a and thefirst transport layer 351 b may be unclear as shown by a dotted line inFIG. 16A. A mixed region of the first transport layer 351 a and thefirst transport layer 351 b is preferably formed so that an energybarrier between the first transport layer 351 a and the first transportlayer 351 b can be changed smoothly. In addition, when the first layer351 is a multilayer and electrons are injected from the electrode 312, alayer including an electron transporting substance and a metal oxidesuch as lithium oxide, calcium oxide or magnesium oxide and a layerincluding only an electron transporting substance may be stacked. Inparticular, in the case where the electron transporting substance tendsto be easily crystallized, crystallization can be prevented by includinga metal oxide and a short circuit between electrodes of thelight-emitting element due to crystallization can be prevented. FIG. 16Ais an enlarged view of the overlapping portion of the electrode 312, thelight-emitting layer 314 and the electrode 315 (a portion surrounded bya dotted line in FIG. 16B).

A second transport layer 352 may be provided between the electrode 315and the light-emitting layer 314 as shown in FIGS. 14A and 14B. Whenelectrons are injected from the electrode 315, the second transportlayer 352 is preferably formed using an electron transporting substance.When holes are injected from the electrode 315, the second transportlayer 352 is preferably formed using a hole transporting substance. Inthis manner, by providing the second transport layer 352, the electrode315 can be prevented from becoming closer to the light-emitting layer314; therefore, quenching of light due to the metal included in theelectrode 315 can be prevented. The second transport layer 352 may be asingle layer or a multilayer including the second transport layer 352 a,the second transport layer 352 b or another layer as shown in FIG. 15A.When the second transport layer 352 is a multilayer and electrons areinjected from the electrode 315, a layer including an electrontransporting substance and a metal oxide such as lithium oxide, calciumoxide or magnesium oxide and a layer including only an electrontransporting substance may be stacked. In particular, in the case wherethe electron transporting substance tends to be easily crystallized,crystallization can be prevented by including the metal oxide and ashort circuit between electrodes of the light-emitting element due tocrystallization can be prevented. The interface between the secondtransport layer 352 a and the second transport layer 352 b may beunclear as shown by a dotted line in FIG. 16A. A mixed region of thesecond transport layer 352 a and the second transport layer 352 b ispreferably formed so that an energy barrier between the second transportlayer 352 a and the second transport layer 352 b can be changedsmoothly. In addition, when the second transport layer 352 is amultilayer and holes are injected from the electrode 315, a layerincluding a hole transporting substance and a metal oxide such asmolybdenum oxide, vanadium oxide or ruthenium oxide and a layerincluding only a hole transporting substance may be stacked. Inparticular, in the case where the hole transporting substance tends tobe easily crystallized, crystallization can be prevented by includingthe metal oxide and a short circuit between electrodes of thelight-emitting element due to crystallization can be prevented.

The interface between the light-emitting layer 314 and the firsttransport layer 351 and the interface between the light-emitting layer314 and the second transport layer 352 may be unclear as shown by adotted line in FIG. 17A. FIG. 17A is an enlarged view of the overlappingportion of the electrode 312, the light-emitting layer 314 and theelectrode 315 (a portion surrounded by a dotted line in FIG. 17B). Amixed region of the light-emitting layer 314 and the first transportlayer 351 b is preferably formed so that an energy barrier between thelight-emitting layer 314 and the first transport layer 351 can bechanged smoothly. Further, a mixed region of the light-emitting layer314 and the second transport layer 352 b is preferably formed so that anenergy barrier between the light-emitting layer 314 and the secondtransport layer 352 can be changed smoothly.

The electrode 315 may be an electrode in which the first layer 315 a andthe second layer 315 b are stacked such that the second layer 315 bexists closer to the light-emitting layer 314 than the first layer 315a. Herein, the second layer 315 b is preferably a layer including ametal oxide and an organic compound. When holes are injected from theelectrode 315, a hole transporting substance is preferably used as theorganic compound and a substance showing electron accepting property tothe hole transporting substance is preferably used as the metal oxide.When electrons are injected from the electrode 315, an electrontransporting substance is preferably used as the organic compound and asubstance selected from substances showing electron donating property tothe electron transporting substance is preferably used as the metaloxide. Further, by adjusting the thickness of the second layer 315 b,the optical path length of emitted light may be adjusted. Light withfavorable color purity can be extracted efficiently by adjusting theoptical path length.

In the light-emitting device described above, light from thelight-emitting layer 314 may be extracted through one side or both sidesof the electrodes 312 and 315. When light is extracted through theelectrode 312 as shown by an outline arrow in FIG. 7A, the first layer312 a is formed using indium tin oxide or the like such that visiblelight can transmit through the first layer. When light is extractedthrough the electrode 315 as shown by an outline arrow in FIG. 7B, theelectrode 315 is formed using indium tin oxide or the like such thatvisible light can transmit through the electrode 315. When light isextracted from opposite sides, i.e., through the electrodes 312 and 315as shown by an outline arrow in FIG. 7C, the first layer 312 a and theelectrode 315 are both formed using indium tin oxide or the like suchthat visible light can transmit through the first layer 312 a and theelectrode 315.

A light-emitting device provided with the light-emitting element 316 ispreferably encapsulated by substrates 301, 320 and a sealing agent 321so as not to expose the light-emitting element 316 to the air, as shownin FIG. 2C. In FIG. 2C, the substrate 301 is bonded to a substrate 320by the sealing agent 321 so as to encapsulate the light-emitting element316. The inside surrounded by substrates 301, 320 and the sealing agent321 is filled with nitrogen, an inert gas, resin or the like. Theconductive layer 307 is connected to a flexible printed circuit 322 by aconductive adhesive agent 323.

The light-emitting device described above is manufactured using asemiconductor device of the present invention; therefore, thelight-emitting layer 314 can cover the electrode 315 with favorablecoverage and a short circuit between the electrodes 312 and 315, or thelike are difficult to be caused. In addition, end portions of theelectrode 312 are covered by the partition layer 313. Thus, defects of alight-emitting element such as a short circuit between the electrodes312 and 315 due to a concentrated electric field at the end portions ofthe electrode 312 can be prevented. As described above, a favorablelight-emitting device in which defects such as a short circuit betweenelectrodes are difficult to be caused, can be manufactured by using asemiconductor device of the present invention.

Embodiment Mode 3

One mode of a semiconductor device of the present invention is explainedwith reference to FIG. 3. An insulating layer 152 is provided on asubstrate 151. Further, a transistor 161 including a semiconductor layer153, a gate insulating layer 154, and a gate electrode 155 is providedover the insulating layer 152. The transistor 161 is covered with theinsulating layers 156 and 157 having opening portions. Conductive layers158 a and 158 b are provided over the insulating layer 156. Moreover,the conductive layers 158 a and 158 b are connected to the semiconductorlayer 153 through the opening portion provided in the gate insulatinglayer 154 and the insulating layer 156 respectively. In addition, anelectrode 159 including a first layer 159 a and a second layer 159 b isprovided over the insulating layer 157. A part of the first layer 159 aof the electrode 159 is stacked on the conductive layer 158 a, and theelectrode 159 is electrically connected to the conductive layer 158 a.In addition, end portions of the electrode 159 are covered with apartition layer 160.

Note that the description of the substrate 101 is referred to for thesubstrate 151, the description of the insulating layer 102 is referredto for the insulating layer 152, the description of the semiconductorlayer 103 is referred to for the semiconductor layer 153, thedescription of the gate insulating layer 104 is referred to for the gateinsulating layer 154, and the description of the gate electrode 105 isreferred to for the gate electrode 155. In addition, the description ofthe insulating layer 106 is referred to for the insulating layer 156,and the description of the insulating layer 108 is referred to for theinsulating layer 157.

The conductive layer 158 a and the electrode 159 may be connectedelectrically by stacking the electrode 159 on the conductive layer 158a, like the semiconductor device shown in FIG. 3.

The first layer 159 a corresponds to the first layer 109 a, and thesecond layer 159 b corresponds to the second layer 109 b. Therefore, thedescription of the first layer 109 a and the second layer 109 b arereferred to for the first layer 159 a and the second layer 159 b,respectively.

Like the semiconductor device shown in FIG. 3, it is possible tomanufacture a light-emitting device in which defects such as a shortcircuit due to the unevenness of the electrode 159 are reduced by usinga semiconductor device in which the electrode 159 including the firstlayer 159 a and the second layer 159 b is formed so that the endportions of the electrode 159 are covered with the partition layer 160.Moreover, a light-emitting device which has almost no defects such asshort circuit or the like due to an electric field caused at endportions of an electrode, can be manufactured.

Embodiment Mode 4

Embodiment Mode 4 explains one mode of a semiconductor device includinga channel-etch type bottom gate transistor of the present invention withreference to FIG. 4.

A transistor 211 including a gate electrode 203, a gate insulating layer204, a first semiconductor layer 205, a second semiconductor layer 206a, and a second semiconductor layer 206 b is provided over a substrate201. The gate electrode 203 is provided over the substrate 201. Inaddition, the gate insulating layer 204 is provided to cover the gateelectrode 203. Further, the first semiconductor layer 205 is provided tobe in contact with the gate insulating layer 204 over an overlappingportion of the gate electrode 203 and the gate insulating layer 204. Thesecond semiconductor layers 206 a and 206 b are each in contact with thefirst semiconductor layer 205, and one of the second semiconductorlayers 206 a and 206 b is provided to serve as a source, and the other,serve as a drain of the transistor. The second semiconductor layer 206 ais stacked over the conductive layer 206 c. Moreover, the conductivelayer 206 d is stacked over the second semiconductor layer 206 b. Aninsulating layer 207 having an opening portion is provided to cover thetransistor 211, the conductive layers 206 c, 206 d and the like. Anelectrode 208 is formed over the insulating layer 207. The electrode 208includes a first layer 208 a and a second layer 208 b, and the firstlayer 208 a is in contact with the insulating layer 207. Further, theelectrode 208 covers the opening portion provided in the insulatinglayer 207, and is in contact with the conductive layer 206 c. Inaddition, a partition layer 209 having an opening portion is provided tocover end portions of the electrode 208 over the insulating layer 207.Further, the electrode 208 is exposed by the opening portion provided inthe partition layer 209.

The electrode 208 can be used as an electrode of a light-emittingelement. Here, the first layer 208 a is formed with a conductivesubstance as well as the first layer 109 a shown in embodiment mode 1.In addition, the second layer 208 b includes a metal oxide and anorganic compound as well as the second layer 109 b shown in EmbodimentMode 1. It is preferable for the first layer 208 a and the second layer208 b to be formed in the same way as the first layer 109 a and thesecond layer 109 b respectively.

In the electrode 208, since the first layer 208 a is covered with thesecond layer 208 b, the unevenness formed on the surface of the firstlayer is reduced so that the electrode has favorable smoothness. It ispossible to manufacture a favorable light-emitting device in whichdefects are reduced such as a short circuit or the like between theelectrodes of the light-emitting element due to the unevenness of theelectrode 208 by using a semiconductor device including such anelectrode of the present invention.

Note that the description of the substrate 101 is referred to for thesubstrate 201, the description of the gate electrode 105 is referred tofor the gate electrode 203, the description of the gate insulating layer104 is referred to for the gate insulating layer 204, and thedescription of the semiconductor layer 103 is referred to for the firstsemiconductor layer 205. The second semiconductor layers 206 a and 206 beach include an n-type impurity and are formed with a semiconductor suchas silicon or silicon germanium. There are no limitations oncrystallinity of the second semiconductor layers 206 a and 206 b, andthe second semiconductor layers 206 a and 206 b may include one or bothof an amorphous semiconductor or a crystalline semiconductor. Thedescription of conductive layers 107 a and 107 b are referred to for theconductive layers 206 c and 206 d. In addition, the description of theinsulating layer 106 is referred to for the insulating layer 207, andthe description of the partition layer 110 is referred to for thepartition layer 209.

Embodiment Mode 5

Embodiment Mode 5 shows one mode of a semiconductor device including achannel-stop type bottom gate transistor of the present invention inFIG. 5.

A transistor 261 including a gate electrode 253, a gate insulating layer254, a first semiconductor layer 255, a second semiconductor layer 257a, and a second semiconductor layer 257 b is provided over a substrate251. The gate electrode 253 is provided over the substrate 251. Inaddition, the gate insulating layer 254 is provided to cover the gateelectrode 253. Further, the first semiconductor layer 255 is provided tobe in contact with the gate insulating layer 254 over the overlappingportion of the gate electrode 253 and the gate insulating layer 254. Thesecond semiconductor layers 257 a and 257 b are each in contact with thefirst semiconductor layer 255, and one of the second semiconductorlayers 257 a and 257 b is provided to serve as a source, and the otherserve as a drain of the transistor. A protective layer 256 is providedover a region where a channel is formed in the first semiconductor layer255. The second semiconductor layer 257 a is stacked over a conductivelayer 257 c. Moreover, a conductive layer 257 d is stacked over thesecond semiconductor layer 257 b. An insulating layer 258 having anopening portion is provided to cover the transistor 261, and theconductive layers 257 c and 257 d. An electrode 259 is provided over theinsulating layer 258. The electrode 259 includes a first layer 259 a anda second layer 259 b, and the first layer 259 a is in contact with theinsulating layer 258. Further, the electrode 259 covers the openingportion provided in the insulating layer 258, and is in contact with theconductive layer 257 c. In addition, a partition layer 260 having anopening portion is provided to cover the end portions of the electrode259 over the insulating layer 258. Moreover, the electrode 259 isexposed by the opening portion provided in the partition layer 260.

As described above, the semiconductor device shown in FIG. 5 includes abottom gate type transistor having a different mode from the one shownin Embodiment Mode 4.

The electrode 259 can be used as an electrode of a light-emittingelement. Here, the first layer 259 a is formed with a conductivesubstance in the same way as the first layer 109 a shown in EmbodimentMode 1. In addition, the second layer 259 b includes a metal oxide andan organic compound in the same way as the second layer 109 b shown inEmbodiment Mode 1. It is preferable for the first layer 259 a and thesecond layer 259 b to be formed in the same way as the first layer 109 aand the second layer 109 b respectively.

In the electrode 259, since the first layer 259 a is covered with thesecond layer 259 b, the unevenness formed on the surface of the firstlayer is reduced so that the electrode has favorable smoothness. It ispossible to manufacture a favorable light-emitting device in whichdefects are reduced such as a short circuit or the like betweenelectrodes of the light-emitting element due to the unevenness of theelectrode 259 by using a semiconductor device including such anelectrode of the present invention.

Note that the description of the substrate 101 is referred to for thesubstrate 251, the description of the gate electrode 105 is referred tofor the gate electrode 253, the description of the gate insulating layer104 is referred to for the gate insulating layer 254, and thedescription of the semiconductor layer 103 is referred to for the firstsemiconductor layer 255. Second semiconductor layers 257 a and 257 beach include an n-type impurity and are formed with a semiconductor suchas silicon or silicon germanium. There are no limitations oncrystallinity of the second semiconductor layers 257 a and 257 b, andthe second semiconductor layers 257 a and 257 b may include one or bothof an amorphous semiconductor or a crystalline semiconductor. Thedescription of conductive layers 107 a and 107 d is referred to for theconductive layers 257 c and 257 d. In addition, the description of theinsulating layer 106 is referred to for the insulating layer 258, andthe description of the partition layer 110 is referred to for thepartition layer 260. In addition, the protective layer 256 has afunction of protecting the first semiconductor layer 255 so that thefirst semiconductor layer 255 is not etched when the secondsemiconductor layers 257 a and 257 b and the conductive layers 257 c and257 d are processed. The protective layer 256 may be formed with siliconnitride or the like.

Embodiment Mode 6

One mode of a light-emitting device using a semiconductor device of thepresent invention shown in FIG. 1 is explained with reference to FIG. 6.The light-emitting device shown in FIG. 6 is manufactured by using asemiconductor device having second layers 109 c, 109 d, and 109 e formedto have different thicknesses from each other.

The first layer 109 a is formed with aluminum or the like and is a layerwith high reflectance. A light-emitting layer 120 a including alight-emitting material emitting reddish light is formed over the secondlayer 109 c. In addition, a light-emitting layer 120 b including alight-emitting material emitting greenish light is provided over thesecond layer 109 d. Further, a light-emitting layer 120 c including alight-emitting material emitting bluish light is provided over thesecond layer 109 e. In addition, an electrode 121 is formed with indiumtin oxide or the like, and can transmit visible light.

Each of light emitted from light-emitting elements 123 a, 123 b, and 123c is extracted from the side of the electrode 121.

The thickness of the second layer 109 c is adjusted depending on awavelength of emitted light so as to extract the light with good colorpurity from the side of the electrode 121. Further, the thickness of thesecond layer 109 d is adjusted depending on a wavelength of emittedlight so as to extract the light with good color purity from the side ofthe electrode 121. In addition, the thickness of the second layer 109 eis adjusted depending on a wavelength of emitted light so as to extractthe light with good color purity from the side of the electrode 121.

As described above, a light-emitting device including a plurality oflight-emitting elements which emit different emission colors can bemanufactured by using a semiconductor device of the present invention.Further, the semiconductor device of the present invention can adjust anoptical path length so as to extract light with good color purity fromeach of light-emitting elements.

Embodiment Mode 7

In Embodiment Mode 7, a circuit configuration and a driving method of alight-emitting device having a display function are explained withreference to FIGS. 8 to 11. The light-emitting device in this embodimentmode is a light-emitting device that is manufactured by a semiconductordevice of the present invention as described in Embodiment Mode 2 or 6.

FIG. 8 is a schematic view of a top face of a light-emitting devicemanufactured by a semiconductor device of the present invention. A pixelportion 6511, a source signal line driver circuit 6512, a writing gatesignal line driver circuit 6513, and an erasing gate signal line drivercircuit 6514 are provided on a substrate 6500 in FIG. 8. The sourcesignal line driver circuit 6512, the writing gate signal line drivercircuit 6513, and the erasing gate signal line driver circuit 6514 areeach connected to an FPC (flexible printed circuit) 6503 that is anexternal input terminal via a wiring group. Each of the source signalline driver circuit 6512, the writing gate signal line driver circuit6513, and the erasing gate signal line driver circuit 6514 receives avideo signal, a clock signal, a start signal, a reset signal, and thelike from the FPC 6503. A printed wiring board (PWB) 6504 is attached tothe FPC 6503. The driver circuit portion is not always required to beprovided on the same substrate as the pixel portion 6511. For example,the driver circuit portion may be formed outside the substrate by usingTCP or the like that is formed by mounting an IC chip on an FPC providedwith a wiring pattern.

In the pixel portion 6511, a plurality of source signal lines extendingin a column direction are arranged in a row direction. Current supplylines are also arranged in the row direction. In the pixel portion 6511,a plurality of gate signal lines extending in the row direction arearranged in the column direction. In the pixel portion 6511, a pluralityof circuits each including a light-emitting element are arranged.

FIG. 9 shows a circuit for operating one pixel. The circuit shown inFIG. 9 includes a first transistor 901, a second transistor 902, and alight-emitting element 903.

Each of the first transistor 901 and the second transistor 902 is athree-terminal element including a gate electrode, a drain region, and asource region, in which a channel region is formed between the drainregion and the source region. Because the source region and the drainregion are interchanged depending on a structure, an operationalcondition or the like of the transistor, it is difficult to distinguishthe source region from the drain region. In this embodiment mode,regions to serve as a source and a drain are referred to as a firstelectrode and a second electrode.

A gate signal line 911 and a writing gate signal line driver circuit 913are provided to be electrically connected or not to be electricallyconnected with each other via a switch 918. The gate signal line 911 andan erasing gate signal line driver circuit 914 are provided to beelectrically connected or not to be electrically connected with eachother via a switch 919. A source signal line 912 is provided to beelectrically connected to either a source signal line driver circuit 915or a power source 916 via a switch 920. A gate of the first transistor901 is electrically connected to the gate signal line 911. The firstelectrode of the first transistor 901 is electrically connected to thesource signal line 912, and the second electrode of the first transistor901 is electrically connected to the gate electrode of the secondtransistor 902. The first electrode of the second transistor 902 iselectrically connected to a current supply line 917, and the secondelectrode of the second transistor 902 is electrically connected to oneelectrode included in the light-emitting element 903. The switch 918 maybe included in the writing gate signal line driver circuit 913. Theswitch 919 may also be included in the erasing gate signal line drivercircuit 914. The switch 920 may also be included in the source signalline driver circuit 915.

The arrangement of a transistor, a light-emitting element and the likein the pixel portion is not necessarily limited. For example, theelements can be arranged as shown in a top view of FIG. 10. In FIG. 10,a first electrode of a first transistor 1001 is connected to a sourcesignal line 1004, and a second electrode of the first transistor 1001 isconnected to a gate electrode of the second transistor 1002. A firstelectrode of the second transistor 1002 is connected to a current supplyline 1005, and a second electrode of the second transistor 1002 isconnected to an electrode 1006 of a light-emitting element. A part of agate signal line 1003 serves as a gate electrode of the first transistor1001.

Next, a driving method is explained. FIG. 11 is an explanatory view ofan operation of a frame with time. In FIG. 11, the abscissa-axisdirection represents time passage, whereas the ordinate-axis directionrepresents scanning stages of a gate signal line.

When an image is displayed with a light-emitting device according to thepresent invention, a rewriting operation and a displaying operation forthe image are repeatedly carried out in a display period. The number ofrewriting operations is not necessarily limited; however, the rewritingoperation is preferably performed approximately sixty times per onesecond so that a person who watches the image does not find flickering.Herein, the period when the operations of rewriting and displaying ofone image (one frame) are carried out is referred to as one frameperiod.

One frame period is time-divided into four sub frame periods 501, 502,503, and 504 including write periods 501 a, 502 a, 503 a, and 504 a, andretention periods 501 b, 502 b, 503 b, and 504 b. A light-emittingelement that receives a light-emission signal emits light in theretention period. The length ratio of the retention period in each ofthe first sub frame period 501, the second sub frame period 502, thethird sub frame period 503, and the fourth sub frame period 504 is2³:2²:2¹:2⁰=8:4:2:1. Accordingly, a 4-bit gray scale can be realized.The number of bits or gray scale levels is not limited thereto. Forinstance, an 8-bit gray scale can be offered by providing eight subframe periods.

An operation in one frame period is explained. Firstly, a writingoperation is carried out from the first row to the last row sequentiallyin the sub frame period 501. Therefore, the starting time of a writeperiod is different depending on the rows. The retention period 501 bstarts in the row where the write period 501 a is completed. In theretention period, a light-emitting element that receives alight-emission signal emits light. The sub frame period 502 starts inthe row where the retention period 501 b is completed, and a writingoperation is carried out from the first row to the last row sequentiallyas is the case with the sub frame period 501. Operations as noted aboveare repeatedly carried out to finish the retention period 504 b of thesub frame period 504. When an operation in the sub frame period 504 isfinished, an operation in the next frame period is started. The sum ofemitting light in each of the sub frame periods is an emitting time ofeach light-emitting element in one frame period. By varying the emittingtime depending on each light-emitting element to be variously combinedin one pixel, various colors can be displayed with different brightnessand chromaticity.

As in the sub frame 504, when a retention period in the row wherewriting has been finished and the retention period has started isintended to be forcibly terminated before finishing the writing of thelast row, an erase period 504 c is preferably provided after theretention period 504 b to control so that the light-emission is forciblystopped. The row where the light-emission is forcibly stopped does notemit light during a fixed period (the period is referred to as anon-light emission period 504 d). Upon finishing the write period of thelast row, the next write period (or a frame period) starts from thefirst row. This makes it possible to prevent from the write period ofthe sub frame 504 from overlapping a write period of the next sub frameperiod.

In this embodiment mode, the sub frame periods 501 to 504 are arrangedin the order from the longest retention period; however, the presentinvention is not limited thereto. For instance, the sub frame periods501 to 504 may be arranged in the order from the shortest retentionperiod. The sub frame periods 501 to 504 may be arranged at randomcombining short sub frame periods and long sub frame periods. The subframe period may be further divided into a plurality of frame periods.That is, scanning of the gate signal line may be carried out a pluralityof times during the period of giving the same video signal.

An operation in a write period and an erase period of a circuit shown inFIG. 9 is explained.

First, an operation in the write period is explained. In the writeperiod, the gate signal line 911 in the n-th row (n is a natural number)is electrically connected to the writing gate signal line driver circuit913 via the switch 918. The gate signal line 911 is not connected to theerasing gate signal line driver circuit 914. The source signal line 912is electrically connected to the source signal line driver circuit 915via the switch 920. A signal is inputted to the gate of the firsttransistor 901 connected to the gate signal line 911 in the n-th row,and the first transistor 901 is turned ON. At this time, video signalsare simultaneously inputted to the source signal lines in the firstcolumn to the last column. Video signals inputted from the source signalline 912 at each column are independent from each other. The videosignal inputted from the source signal line 912 is inputted to the gateelectrode of the second transistor 902 via the first transistor 901connected to each source signal line. At this time, the signal inputtedto the second transistor 902 determines a value of a current supplied tothe light-emitting element 903 from a current supply line 917. Emissionor non-emission of the light-emitting element 903 is determineddepending on the current value. For example, in the case that the secondtransistor 902 is a p-channel type, the light-emitting element 903 emitslight when a Low Level signal is inputted to the gate electrode of thesecond transistor 902. On the other hand, in the case that the secondtransistor 902 is an n-channel type, the light-emitting element 903emits light when a High Level signal is inputted to the gate electrodeof the second transistor 902.

Then, an operation in the erase period is explained. In the eraseperiod, the gate signal line 911 of the n-th row (n is a natural number)is electrically connected to the erasing gate signal line driver circuit914 via the switch 919. The gate signal line 911 is not connected to thewriting gate signal line driver circuit 913. The source signal line 912is electrically connected to the power source 916 via the switch 920. Asignal is inputted to the gate of the first transistor 901 connected tothe gate signal line 911 in the n-th row, and the first transistor 901is turned ON. At this time, erase signals are simultaneously inputted tothe source signal lines in the first column to the last column. Theerase signal inputted from the source signal line 912 is inputted to thegate electrode of the second transistor 902 via the first transistor 901connected to each source signal line. By the signal inputted to thesecond transistor 902, current supply from the current supply line 917to the light-emitting element 903 is stopped. The light-emitting element903 does not emit light forcibly. For example, in the case that thesecond transistor 902 is a p-channel type, the light-emitting element903 does not emit light when a High Level signal is inputted to the gateelectrode of the second transistor 902. On the other hand, in the casethat the second transistor 902 is an n-channel type, the light-emittingelement 903 does not emit light when a Low Level signal is inputted tothe gate electrode of the second transistor 902.

In the erase period, a signal for erasing is inputted to the n-th (n isa natural number) row by the operation as described above. However,there is a case that the n-th row is in an erase period and another row(the m-th row, m is a natural number) is in a write period. In thisinstance, it is required that a signal for erasing is inputted to then-th row and a signal for writing is inputted to the m-th row byutilizing a source signal line of the same column. Accordingly, anoperation explained as follows is preferably carried out.

Immediately after the light-emitting element 903 in the n-th row isbrought into a non emission state by the operation in the erase statedescribed above, the gate signal line 911 is disconnected from theerasing gate signal line driver circuit 914, and the source signal line912 is connected to the source signal line driver circuit 915 bychanging the switch 920. As well as connecting the source signal line912 to the source signal line driver circuit 915, the gate signal line911 is connected to the writing gate signal line driver circuit 913. Asignal is selectively inputted to the signal line in the m-th row fromthe writing gate signal line driver circuit 913, and when the firsttransistor is turned ON, signals for writing are inputted to the sourcesignal lines in the first column to the last column from the sourcesignal line driver circuit 915. The light-emitting element in the m-throw emits light or no light depending on the signal.

Immediately after finishing the write period of the m-th row as notedabove, an erase period in the (n+1)-th row starts. Hence, the gatesignal line 911 and the writing gate signal line driver circuit 913 aredisconnected, and the source signal line 912 and the power source 916are connected by changing the switch 920. Further, the gate signal line911 and the writing gate signal line driver circuit 913 aredisconnected, and the gate signal line 911 is connected to the erasinggate signal line driver circuit 914. When a signal is selectivelyinputted to the gate signal line in the (n+1)-th row from the erasinggate signal line driver circuit 914, and the first transistor 901 isturned ON, an erase signal is inputted from the power source 916.Immediately after finishing the erase period in the (n+1)-th row, awrite period in the (m+1)-th row starts. Hereinafter, an erase periodand a write period may be carried out repeatedly to operate to completean erase period of the last row.

In this embodiment mode, a mode in which the write period in the m-throw is provided between the erase period of the n-th row and the eraseperiod of the (n+1)-th row is explained. Without being limited to this,however, the write period of the m-th row may be provided between theerase period at (n−1)-th row and the erase period in the n-th row.

In this embodiment mode, when providing the non-light emission period504 d as in the sub frame period 504, an operation of disconnecting theerasing gate signal line driver circuit 914 from a certain gate signalline and connecting the writing gate signal line driver circuit 913 toanother gate signal line is repeatedly carried out. Such an operationmay be carried out in a frame period that is not provided with anon-light emission period.

Embodiment Mode 8

Electronic devices each having a light-emitting device or the likemanufactured using a semiconductor device of the present invention aredescribed. The light-emitting device incorporated in the electronicdevices described in this embodiment mode is formed according to thepresent invention, operation defects due to a short circuit betweenelectrodes of a light-emitting element can be suppressed. Thus, thelight-emitting device can display a favorable image. Therefore, theelectronic device incorporating such a light-emitting device can providevarious types of information to users, without lack of information ormisconception caused by a fuzzy image.

FIG. 12A illustrates a lap top personal computer manufactured accordingto the present invention. The lap top personal computer includes a mainbody 5521, a casing 5522, a display portion 5523, a keyboard 5524, andthe like. The personal computer can be completed by incorporating alight-emitting device formed using a semiconductor device of the presentinvention as the display portion.

FIG. 12B illustrates a telephone set manufactured according to thepresent invention. The telephone set includes a main body 5552, adisplay portion 5551, a sound output portion 5554, a sound input portion5555, operation switches 5556, 5557, an antenna 5553, and the like. Thetelephone set can be completed by incorporating a light-emitting deviceformed using a semiconductor device of the present invention as thedisplay portion.

FIG. 12C illustrates a television set manufactured according to thepresent invention. The television set includes a display portion 5531, acasing 5532, a speaker 5533, and the like. The television set can becompleted by incorporating a light-emitting device formed using asemiconductor device of the present invention as the display portion.

As noted above, the light-emitting device according to the presentinvention is extremely suitable to be used as a display portion ofvarious kinds of electronic devices.

The personal computer, the telephone set and the television set areexplained in this embodiment mode. Besides, a light-emitting deviceformed using a semiconductor device of the present invention may bemounted to a navigation system, a lighting system, and the like.

This application is based on Japanese Patent Application serial no.2004-318703 filed in Japan Patent Office on 2 Nov. 2004, the entirecontents of which are hereby incorporated by reference.

What is claim is:
 1. A semiconductor device comprising: a transistor; a first electrode electrically connected to the transistor and serving as an electrode of a light-emitting element, the first electrode comprising a first layer and a second layer over the first layer; and a partition layer covering an end portion of the first electrode and comprising an opening portion to expose a part of the second layer, wherein the first layer comprises a conductive substance, wherein the second layer comprises an electron transporting substance and a substance showing electron donating property to the electron transporting substance, and wherein the partition layer is in contact with a top surface of the second layer.
 2. The semiconductor device according to claim 1, wherein the second layer is 100 nm to 300 nm thick.
 3. The semiconductor device according to claim 1, wherein the substance showing electron donating property is one selected from lithium oxide, calcium oxide and magnesium oxide.
 4. A light-emitting device comprising: a semiconductor device according to claim 1; a light-emitting layer; and a second electrode, wherein the first electrode, the light-emitting layer and the second electrode are overlapped with each other.
 5. The light-emitting device according to claim 4, wherein the second layer is 100 nm to 300 nm thick.
 6. An electronic device using the light-emitting device according to claim 4 in a display portion.
 7. The light-emitting device according to claim 4, wherein the substance showing electron donating property is one selected from lithium oxide, calcium oxide and magnesium oxide.
 8. The semiconductor device according to claim 1, further comprising an insulating layer over the transistor, wherein the first layer is in contact with the insulating layer.
 9. A semiconductor device comprising: a first transistor; a first electrode electrically connected to the first transistor and serving as an electrode of a first light-emitting element; a second transistor; a second electrode electrically connected to the second transistor and serving as an electrode of a second light-emitting element; and a partition layer covering an end portion of the first electrode and an end portion of the second electrode, wherein each of the first electrode and the second electrode comprises: a first layer comprising a conductive substance; and a second layer over the first layer, the second layer comprising an electron transporting substance and a substance showing electron donating property to the electron transporting substance, wherein the partition layer comprises at least a first opening portion to expose a part of the second layer of the first electrode and a second opening portion to expose a part of the second layer of the second electrode, wherein the partition layer is in contact with a top surface of the second layer of the first electrode and a top surface of the second layer of the second electrode, and wherein an emission color of the first light-emitting element is different from an emission color of the second light-emitting element and a thickness of the second layer of the first electrode is different from a thickness of the second layer of the second electrode.
 10. The semiconductor device according to claim 9, wherein the second layer is 100 nm to 300 nm thick.
 11. The semiconductor device according to claim 9, wherein the substance showing electron donating property is one selected from lithium oxide, calcium oxide and magnesium oxide.
 12. The semiconductor device according to claim 9, further comprising an insulating layer over the first transistor and the second transistor, wherein the first layer of the first electrode and the first layer of the second electrode are in contact with the insulating layer. 